Structure and Magnetism of a Spin Ladder System: (C5H9NH3)2CuBr4

Low-Temperature Ferromagnetic Order in a Two-Level Layered Co2+ Material

The magnetic properties of a 2D layered material consisting of high-spin Co2+ complexes, [Co(NH3NH2)2(H2O)2Cl2]Cl2 (CoHyd 2 Cl 4 ), have been extensively characterized using electron paramagnetic resonance, magnetic susceptibility, and low-temperature heat capacity measurements. Electron paramagnetic resonance spectroscopy studies suggest that below 50 K, the J = 3/2 orbital triplet state of Co is gradually depopulated in favor of the J = 1/2 spin state, which is dominant below 20 K. In light of this, the magnetic susceptibility has been fitted with a two-level model, indicating that the interactions in this material are much weaker than previously thought. This two-level model is unable to fit the data at low temperatures and, combined with electron paramagnetic resonance spectroscopy, suggests that ferromagnetic interactions between Co2+ cations in the J = 1/2 state become significant approaching 2 K. Heat capacity measurements suggest the emergence of a long-range ordered state below 246 mK, which neutron diffraction confirms to be ferromagnetic.

Quantum Spin‐1/2 Dimers in a Low‐Dimensional Tetrabromocuprate Magnet

This work describes a homometallic spin‐1/2 tetrabromocuprate adopting a bilayer structure. Magnetic‐susceptibility measurements show a broad maximum centred near 70 K, with fits to this data using a Heisenberg model consistent with strong antiferromagnetic coupling between neighbouring copper atoms in different layers of the bilayer. There are further weak intralayer ferromagnetic interactions between copper cations in neighbouring dimers. First‐principles calculations are consistent with this, but suggest there is only significant magnetic coupling within one direction of a layer; this would suggest the presence of a spin ladder within the bilayer with antiferromagnetic rung and weaker ferromagnetic rail couplings.

Low-Dimensional Metal Halide Perovskite Crystal Materials: Structure Strategies and Luminescence Applications

Replacing methylammonium (MA+ ), formamidine (FA+ ), and/or cesium (Cs+ ) in 3D metal halide perovskites by larger organic cations have built a series of low-dimensional metal halide perovskites (LDMHPs) in which the inorganic metal halide octahedra arranging in the forms of 2D layers, 1D chains, and 0D points. These LDMHPs exhibit significantly different optoelectronic properties from 3D metal halide perovskites (MHPs) due to their unique quantum confinement effects and large exciton binding energies. In particular, LDMHPs often have excellent broadband luminescence from self-trapped excitons. Chemical composition, hydrogen bonding, and external factors (temperature and pressure etc.) determine structures and influence photoelectric properties of LDMHPs greatly, and especially it seems that there is no definite regulation to predict the structure and photoelectric properties when a random cation, metal, and halide is chosen to design a LDMHP. Therefore, this review discusses the construction strategies of the recent reported LDMHPs and their application progress in the luminescence field for a better understanding of these factors and a prospect for LDMHPs' development in the future.

A spin-1/2 gapped compound CdCu2(SeO3)2Cl2 with a ladder structure

The exploration of two-leg spin-ladder materials is a great challenge to the chemical community since it is one of the most ideal models for the study of low-dimensional magnetism and high-Tc superconductivity. Herein, we report on a successful synthesis of a new Cu2+-based two-leg ladder compound constructed by CuO4Cl2 octahedra along the [101] direction. The magnetic results exhibit a broad peak at Tmax ∼ 265 K, and suggest that CdCu2(SeO3)2Cl2 has a spin singlet ground state. The fitting of the isolated two-leg spin-ladder model shows J⊥/kB = 429 K and J‖/kB = 21 K, leading to a large spin gap of ∼409 K.

Low dimensional and frustrated antiferromagnetic interactions in transition metal chloride complexes with simple amine ligands

New transition metal chloride complexes with hydrazinium and methylhydroxylamine ligands are reported featuring low dimensional and frustrated magnetic interactions.

Spin-singlet Quantum Ground State in Zigzag Spin Ladder Cu(CF3 COO)2

The copper salt of trifluoroacetic acid, Cu(CF₃ COO)₂ , offers a new platform to investigate the quantum ground states of low-dimensional magnets. In practice, it realizes the ideal case of a solid hosting essentially isolated magnetic monolayers. These entities are constituted by well-separated two-leg half-integer spin ladders organized in a zigzag fashion. The ladders are comprised of dimeric units of edge-sharing tetragonal pyramids coupled through carbon ions. The spin-gap state in this compound was revealed by static and dynamic magnetic measurements. No indications of long range magnetic ordering down to liquid helium temperature were obtained in specific heat measurements. First principles calculations allow estimation of the main exchange interaction parameters, J_⊥ =176 K and J_∥ =12 K, consistent with the weakly interacting dimers model.

New organically templated thiocyanatocadmates and chlorocuprate(II): synthesis and structural characterization

With various organic base molecules as the countercations, five new thiocyanatocadmates [H2(tmen)][Cd(SCN)4] (tmen = N,N,N',N'-tetramethylethylenediamine) 1, [H2(tmba)][Cd2(SCN)6] (tmba = N,N,N',N'-tetramethyl-1,4-butanediamine) 2, [H2(teen)][Cd2(SCN)6] (teen = N,N,N',N'-tetra-ethylethylenediamine) 3, [H(amp)][Cd(SCN)2(CH3COO)] (amp = 2-amino-6-methylpyridine) 4 and [H(abp)]4[Cd(SCN)4]SO4·H2O (abp = 2-amino-6-bromopyridine) 5, and one new chlorocuprate(II) [H2(cha)][CuCl4] (cha = 1,4-cyclohexanediamine) 6 were obtained from a series of simple room-temperature self-assemblies at pH = 2 or 6.5. X-ray single-crystal diffraction analysis reveals that (i) templated by [(CH3)2NH(CH2)2NH(CH3)2](2+) (H2(tmen)(2+)), the anion [Cd(SCN)4](2-) in 1 shows a 1-D linear single-chain structure, whereas templated by [(CH3)2NH(CH2)4NH(CH3)2](2+) (H2(tmba)(2+)), the anion [Cd2(SCN)6](2-) in 2 shows a 1-D linear double-chain structure. The number of C atoms between the two N atoms in the templating agent controls the width of the anionic chain through the N(amino)-H···N(SCN) interactions; (ii) templated by [(C2H5)2NH(CH2)2NH(C2H5)2](2+) (H2(teen)(2+)), the anion [Cd2(SCN)6](2-) in 3 exhibits a 3-D open-framework structure, which is based on zigzag anionic chains. A direct change of the substituent group from -CH3 to -C2H5 alters indirectly the shape of the anionic chain from a linear shape to a zigzag shape; (iii) 4 shows a 3-D supramolecular network structure, which is built up from the 1-D zigzag anionic structures by the H(amp)(+) molecules via N-H···O interactions. The formation of the zigzag chain derives from the chelation of the CH3COO(-) groups to the Cd(2+) centers; (iv) 5 is indeed a double salt of [H(abp)]2[Cd(SCN)4] and [H(abp)]2SO4. SO4(2-) and H(abp)(+) form a supramolecular aggregation. Surrounded by the aggregations, the anion [Cd(SCN)4](2-) only shows a dinuclear structure; and (v) templated by H2(cha)(2+), the anion [CuCl4](2-) in 6 displays a 2-D perovskite layer structure. The photoluminescence analysis indicates that upon excitation (λ(ex) = 335 nm for 4, λ(ex) = 395 nm for 5), and emit light (λ(em) = 365 nm for 4, λ(em) = 470 nm for 5), which can be seen clearly under the UV lamp.

A magnetically isolated cuprate spin-ladder system: synthesis, structures, and magnetic properties

Two magnetically isolated cuprate spin ladders have been synthesized. Their crystal structures and preliminary investigation into the magnetic properties were reported.

A trimethylsulfonium salt with a novel polymeric cadmate anion

The title salt, catena-poly[trimethylsulfonium [μ2-chlorido-di-μ2-thiocyanato-cadmate(II)]] {(C3H9S)[CdCl(NCS)2]}n, consists of trimethylsulfonium cations sandwiched between layers of a two-dimensional polyanion. The Cd(II) centre displays a distorted octahedral environment coordinated by two bridging Cl atoms, two thiocyanate N atoms and two thiocyanate S atoms. The thiocyanate groups adopt the μ-1,3-coordination mode and bridge the Cd(II) centres into a one-dimensional zigzag chain extended along the [110] direction. The Cd(II) centres of the zigzag chains are crosslinked by bridging Cl atoms, forming a two-dimensional polyanion. The two-dimensional anions are linked to layers of trimethylsulfonium cations by weak intermolecular C-H···Cl hydrogen bonds, forming the three-dimensional structure.

Bis(cyclohexylammonium) tetrabromidocuprate(II)

The structure of the title salt, (C₆H₁₄N)₂[CuBr₄], is built up from cyclo­hexyl­ammonium cations and tetra­bromidocuprate anions, the latter being located on an inversion center. In the crystal, anions and cations are inter­connected by N—H⋯Br hydrogen bonds, forming ribbons parallel to [0-11].

Crystal structure and carrier transport properties of a new 3D mixed-valence Cu(I)-Cu(II) coordination polymer including pyrrolidine dithiocarbamate ligand

A novel mixed-valence Cu(i)-Cu(ii) coordination polymer having an infinite three-dimensional (3D) structure, {[Cu(I)(4)Cu(II)(2)Br(4)(Pyr-dtc)(4)]·CHCl(3)}(n) (1) (Pyr-dtc(-) = pyrrolidine dithiocarbamate), has been prepared and structurally characterized via X-ray diffraction. This complex consists of 1D Cu(i)-Br chains and bridging mononuclear copper(ii) units of Cu(II)(Pyr-dtc)(2), which form an infinite 3D network. A magnetic study indicates that this complex includes copper(ii) ions exhibiting a weak antiferromagnetic interaction (θ = -0.086 K) between the unpaired electrons of the copper(ii) ions present in the diamagnetic Cu(i)-Br chains. The carrier transport properties of 1 are investigated using an impedance spectroscopy technique and flash-photolysis time-resolved microwave conductivity measurement (FP-TRMC). The impedance spectroscopy reveals that this complex exhibits intriguing semiconducting properties at a small activation energy (E(a) = 0.29 eV (bulk)). The sum of the mobilities of the negative and positive carriers estimated via FP-TRMC is Σμ∼ 0.4 cm(2) V(-1) s(-1).

Field-controlled Luttinger liquid and possible crossover into spin liquid in strong-rail ladder systems

The thermodynamics and transport properties of strong-rail ladder systems are investigated by means of Green's function theory. It is shown that the magnetic behavior clearly manifests a typical antiferromagnetism with gapped or gapless low-lying excitations, which is in agreement with the experimental results. In addition, the temperature-field-induced phase diagram is explored, and we demonstrate a Luttinger liquid behavior in the window h(c) (marking the ending of the M=0 plateau)<h<h(s) (saturation magnetic field) within a narrow range of temperature. The spin liquid phase is uncovered for h<h(c) upon cooling down to zero temperature. It is also shown that the rung entanglement entropy is a good indicator for detecting the field-driven quantum criticality. Meanwhile, the magnetic susceptibility, the specific heat, and the thermal (spin) Drude weights are calculated to characterize the plentiful quantum phases, in which the thermal insulating and conducting behaviors can be controlled by magnetic fields.

Cobalt diphosphonate with a new double chain structure exhibiting field-induced magnetic transition

A cobalt diphosphonate Co(H(2)O){C(5)H(5)N-CH(2)CH(OH)(PO(3))(PO(3)H)} (1) has been synthesized under hydrothermal conditions. It shows a novel type of double chain structure in which one of the two CPO(3) terminus caps on top of the {Co(2)(micro-O)2} dimer while the other connects the adjacent {Co(2)(micro-O)2} dimers into a chain. The magnetization measurements reveal that dominant antiferromagnetic interactions are mediated between the magnetic centers and the compound experiences a field-induced magnetic transition at low temperature with H(c) of ca. 15 kOe at 1.8 K.

The Nature of Halogen···Halide Synthons: Theoretical and Crystallographic Studies

Two types of halogen...halide synthons are investigated on the basis of theoretical and crystallographic studies; the simple halogen...halide synthons and the charge assisted halogen...halide synthons. The former interactions were investigated theoretically (ab initio) by studying the energy of interaction of a halide anion with a halocarbon species as a function of Y...X- separation distance and the C-Y...X- angle in a series of complexes (R-Y...X-, R=methyl, phenyl, acetyl or pyridyl; Y=F, Cl, Br, or I; X-=F-, Cl-, Br-, or I-). The theoretical study of the latter interaction type was investigated in only one system, the [(4BP)Cl]2 dimer, (4BP=4-bromopyrdinium cation). Crystal structure determinations, to complement the latter theoretical calculations, were performed on 13 n-chloropyridinium and n-bromopyridinium halide salts (n=2-4). The theoretical and crystallographic studies indicate that these interactions are controlled by electrostatics and are characterized by linear C-Y...X- angles and separation distances less than the sum of van der Waals radius (rvdW) of the halogen atom and the ionic radii of the halide anion. The strength of these contacts from calculations varies from weak or absent, e.g., H3C-Cl...I-, to very strong, e.g., HCC-I...F- (energy of interaction ca. -153 kJ/mol). The strengths of these contacts are influenced by four factors: (a) the type of the halide anion; (b) the type of the halogen atom; (c) the hybridization of the ipso carbon; (d) the nature of the functional groups. The calculations also show that charge assisted halogen...halide synthons have a comparable strength to simple halogen...halide synthons. The nature of these contacts is explained on the basis of an electrostatic model.

Synthesis, Structure, and Magnetic Properties of an Antiferromagnetic Spin-Ladder Complex: Bis(2,3-dimethylpyridinium) Tetrabromocuprate

The complex (2,3-dmpyH)2CuBr4 has been synthesized and its crystal packing determined by single-crystal X-ray diffraction (2,3-dmpyH = 2,3-dimethylpyridinium). The compound crystallizes in the triclinic space group P1. The crystal packing is characterized by the formation of a ladder structure for the CuBr4 anions showing short Br...Br contacts. The rungs of the ladder are formed via a crystallographic inversion center, while the rails are formed via unit cell translations. Variable temperature magnetic susceptibility measurements agree very well with the ladder model [Jrung = -3.10 cm-1 (-4.34 K) and Jrail = -6.02 cm-1 (-8.42 K)]. The assignment as a magnetic ladder is confirmed by first principles bottom-up theoretical calculations which conclude that Jrung = -3.49 cm-1 (-4.89 K) and Jrail = -7.79 cm-1 (-10.9 K), in very good agreement with the experimental values. They also support the absence of additional significant magnetic exchange within the crystals. Thus, (2,3-dmpyH)2CuBr4 represents the second reported example of a weak-exchange limit magnetic ladder (that is, one in which the exchange along the rail is stronger than that across the rung).

Dimethylammonium trichlorocuprate(II): structural transition, low-temperature crystal structure, and unusual two-magnetic chain structure dictated by nonbonding chloride-chloride contacts

Catena(dimethylammonium-bis(mu2-chloro)-chlorocuprate), (CH3)2NH2CuCl3, forms chains of Cu2Cl6(2-) bifold dimers linked along the structural chain axis by terminal chlorides forming long semicoordinate bonds to adjacent dimers. The structural chains are separated by dimethylammonium ions that hydrogen bond to chloride ions of the dimers. A structural phase transition below room temperature removes disorder in the hydrogen bonding, leaving adjacent dimers along the chain structurally and magnetically inequivalent, with alternating ferromagnetic and antiferromagnetic pairs. The coupled dimers are magnetically isolated from each other along the structural chain axis by the long semicoordinate Cu-Cl bond. However, the dimers couple to like counterparts on adjacent chains via nonbonding Cl...Cl contacts. The result is two independent magnetic chains, one an alternating antiferromagnetic chain and the other an antiferromagnetic chain of ferromagnetically coupled copper dimers, which run perpendicular to the structural chains. This magnetostructural analysis is used to fit unusual low-temperature (1.6 K) magnetization vs field data that display a two-step saturation. The structural phase transition is identified with neutron scattering and capacitance measurements, and the X-ray crystal structures are determined at room temperature and 84 K. The results appear to resolve long-standing confusion about the origins of the magnetic behavior of this compound and provide a compelling example of the importance of two-halide magnetic exchange.

Double-Stranded Metal−Organic Networks for One-Dimensional Mixed Valence Coordination Polymers

The design of new types of metal-organic networks and the search for unusual crystal architecture represents an important task for modern inorganic and materials chemistry research. A group of new monosubstituted phenylcyanoximes, containing F, Cl, and Br atoms at the 2, 3, or 4 positions, were synthesized using the high yield nitrosation reaction with CH3-ONO and were spectroscopically (1H NMR, 13C NMR, UV-visible, IR, mass spectrometry) and structurally characterized. Results of X-ray analysis revealed nonplanar trans-anti geometry for 2-chlorophenyl(oximino)acetonitrile, H(2Cl-PhCO); a nonplanar anti configuration for 4-chlorophenyl(oximino)acetonitrile, H(4Cl-PhCO); and planar cis-syn geometry for 3-fluorophenyl(oximino)acetonitrile, H(3F-PhCO). All arylcyanoximes undergo deprotonation in solutions with the formation of colored anions exhibiting pronounced negative solvatochromism in a series of polar protic and aprotic solvents. Nine thallium(I) cyanoximates were obtained using the reaction between hot (approximately 95 degrees C) aqueous solutions of Tl2CO3 and solid powdery monohalogenated arylcyanoximes HL. Crystal structures of two Tl(I) cyanoximates [Tl(2Cl-PhCO) and Tl(4Br-PhCO)] contained centrosymmetric dimeric units (TlL)2 that are connected to a coordination polymer by means of an oxygen atom of the oxime group of the neighboring molecule. Cyanoxime anions act as bridging ligands in both structures where the polymeric motif consists of double-stranded Tl-O chains interconnected with the formation of zigzagging Tl2O2 planar rhombes. Thallium atoms form infinite linear arrays with close intermetallic separations. The nearest Tl(I)...Tl(I) distances are 3.838 and 4.058 angstroms in the Tl(2Cl-PhCO) and Tl(4Br-PhCO) structures, respectively, close to that in metallic thallium (3.456 angstroms). Monosubstituted phenyl groups are well aligned in pi-stacking columns that are perpendicular to the array of Tl(I) atoms and stabilize formed structures. Coordination polyhedrons of thallium(I) in these complexes represent distorted trigonal pyramids with stereoactive lone pair.